July 7, 2011
Open letter to be posted on nobabies.net

James R. Usherwood
Structure and Motion Laboratory
The Royal Veterinary College
University of London
North Mymms
Hatfield AL9 7TA

Dear James Usherwood:
I enjoyed your article.  (James R. Usherwood Flying in a Flock Comes at a Cost in Pigeons NATURE vol. 474 no. 7352 June 23, 2011 page 494)  I was particularly intrigued by the enigma you posed: while some birds that fly in strict formation seem to gain an efficiency advantage, pigeons are less organized and flocking is an energy cost, so why do they?

Let me try.

Any system has mass, energy and information that might be managed.  Life manages all three.  Mass seems irrelevant to your question, and you have already neatly addressed the energy issue and found it paradoxical, so the resolution must be that there is an advantage in information management. 

Perhaps flocking produces an advantage of pooled observation and/or pooled experience.  But there is a third possibility.

In birds and mammals as well as other animals, there appears to be a fertility advantage to maintaining a small gene pool size.  A small population will grow rapidly, a smaller one slower and a fair sized one will decline, and this effect does not appear to be due to any environmental effect.  (R. Sibly et al., Science 309, 607 (2005)) Exactly the same effect is demonstrable in humans, but humans do no fly in flocks. 

I propose that the information being managed is that the birds are keeping track of each other.  That way they can control their mate selection and keep their gene pool small and vigorous. 

It is a happy coincidence that the issue should come up in pigeons.  Charles Darwin in his book Origin of Species spends most of his time talking about pigeons and reserves a single sentence to the origin of species, the gist of which is that he has no idea at all.  “Happenstance,” is his lame remark.  Had he laid aside his pen and gone to a park to look at some free pigeons he might have noticed, as anyone can, that where people are feeding pigeons the pigeons are all fat.  Malthus, upon whom Darwin doted, would have predicted that absent such factors as predators, which are not much in evidence in parks, the pigeon population should increase until they are all starving.  That apparent contradiction is of course due to the failure of fertility as the flock exceeds the size of design limits. 

If you wish to see the logic behind this, look at the poster I presented at Vancouver this year.  It is on nobabies.net about March 18.  If you are interested, of course I am at your disposal for any further explanation. 

If you pursue this I am pretty sure that, right or wrong, you will get a very cold reception.  This of course gets rather far from “Structure and Motion,” but you did raise the question, and since you had the courage to do that, perhaps your courage is unlimited. 


M. Linton Herbert MD 

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